U.S. patent application number 17/632692 was filed with the patent office on 2022-09-08 for electro-luminescent material and electro-luminescent device.
This patent application is currently assigned to NEXDOT. The applicant listed for this patent is NEXDOT. Invention is credited to Michele D'AMICO, Alexis KUNTZMANN, Yu-Pu LIN, Vladyslav VAKARIN.
Application Number | 20220282152 17/632692 |
Document ID | / |
Family ID | 1000006416358 |
Filed Date | 2022-09-08 |
United States Patent
Application |
20220282152 |
Kind Code |
A1 |
D'AMICO; Michele ; et
al. |
September 8, 2022 |
ELECTRO-LUMINESCENT MATERIAL AND ELECTRO-LUMINESCENT DEVICE
Abstract
An electro-luminescent film including a substrate and
anisotropic semiconductor nanoparticles distributed on the
substrate according to a periodic pattern. The semiconductor
nanoparticles have an aspect ratio greater than 1.5, and the
repetition unit of the pattern has a smallest dimension of less
than 500 micrometer and includes at least one pixel. Also, a
process for the manufacture of the electro-luminescent film, and a
light emitting device that includes the electro-luminescent
film.
Inventors: |
D'AMICO; Michele;
(Romainville, FR) ; KUNTZMANN; Alexis; (Clichy La
Garenne, FR) ; LIN; Yu-Pu; (Versailles, FR) ;
VAKARIN; Vladyslav; (Palaiseau, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEXDOT |
Romainville |
|
FR |
|
|
Assignee: |
NEXDOT
Romainville
FR
|
Family ID: |
1000006416358 |
Appl. No.: |
17/632692 |
Filed: |
July 31, 2020 |
PCT Filed: |
July 31, 2020 |
PCT NO: |
PCT/EP2020/071651 |
371 Date: |
February 3, 2022 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 11/883 20130101;
H05B 33/145 20130101; C09K 11/025 20130101; C09K 11/565
20130101 |
International
Class: |
C09K 11/88 20060101
C09K011/88; C09K 11/56 20060101 C09K011/56; C09K 11/02 20060101
C09K011/02; H05B 33/14 20060101 H05B033/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 2019 |
EP |
19190095.0 |
Claims
1.-14. (canceled)
15. An electro-luminescent film comprising a substrate and
semiconductor nanoparticles distributed on the substrate according
to a periodic pattern, wherein semiconductor nanoparticles have an
aspect ratio greater than 1.5; wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least one pixel.
16. The electro-luminescent film according to claim 15, wherein the
pattern is periodic in two dimensions.
17. The electro-luminescent film according to claim 16, wherein the
periodic pattern is a rectangular lattice or a square lattice.
18. The electro-luminescent film according to claim 15, wherein
semiconductor nanoparticles are inorganic.
19. The electro-luminescent film according to claim 18, wherein
semiconductor nanoparticles are semiconductor nanocrystals
comprising a material of formula M.sub.xQ.sub.yE.sub.zA.sub.w,
wherein: M is selected from the group consisting of Zn, Cd, Hg, Cu,
Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd,
Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb,
As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Cs; Q is selected from the group consisting of Zn, Cd, Hg, Cu,
Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd,
Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb,
As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Cs; E is selected from the group consisting of O, S, Se, Te, C,
N, P, As, Sb, F, Cl, Br, I; A is selected from the group consisting
of O, S, Se, Te, C, N, P, As, Sb, F, Cl, Br, I; and x, y, z and w
are independently a rational number from 0 to 5; x, y, z and w are
not simultaneously equal to 0; x and y are not simultaneously equal
to 0; z and w are not simultaneously equal to 0.
20. The electro-luminescent film according to claim 15, wherein
semiconductor nanoparticles have a longest dimension greater than
25 nanometers.
21. The electro-luminescent film according to claim 15, wherein
semiconductor nanoparticles have a longest dimension greater than
35 nanometers.
22. The electro-luminescent film according to claim 15, wherein
semiconductor nanoparticles are on the substrate with their longest
dimension substantially aligned in a predetermined direction.
23. The electro-luminescent film according to claim 15, wherein
substrate is selected from a conductive material and a
semi-conductive material.
24. The electro-luminescent film according to claim 15, wherein
semiconductor nanoparticles on the substrate form layers with a
thickness of less than 100 nm.
25. The electro-luminescent film according to claim 15, wherein the
repetition unit of the periodic pattern comprises at least two
pixels.
26. The electro-luminescent film according to claim 25, wherein
semiconductor nanoparticles on the first pixel of the at least two
pixels are different from semiconductor nanoparticles on the second
pixel of the at least two pixels.
27. A process for the manufacture of an electro-luminescent film
comprising a substrate and semiconductor nanoparticles distributed
on the substrate according to a periodic pattern, wherein the
repetition unit of the pattern has a smallest dimension of less
than 500 micrometer and comprises at least one pixel comprising the
steps of: i) providing a substrate; ii) creating a surface electric
potential on the substrate according to the pattern, so that at
least one pixel of the repetition unit is created in the whole
pattern; and iii) bringing the substrate in contact with a
colloidal dispersion of semiconductor nanoparticles having an
aspect ratio greater than 1.5 for a contacting time of less than 15
minutes.
28. The process for the manufacture of an electro-luminescent film
according to claim 27, wherein the substrate is an electret
substrate and wherein the surface electric potential is written on
the electret substrate.
29. The process for the manufacture of an electro-luminescent film
according to claim 28, wherein the repetition unit of the pattern
comprises at least two pixels and wherein semiconductor
nanoparticles on the first pixel of the at least two pixels are
different from semiconductor nanoparticles on the second pixel of
the at least two pixels; and wherein process further comprises: iv)
drying the electret substrate and semiconductor nanoparticles
deposited thereon to form an intermediate structure; v) writing a
surface electric potential on the intermediate structure according
to the pattern, so that the second pixel of the repetition unit is
written in the whole pattern; and vi) bringing the electret
substrate in contact with a colloidal dispersion of semiconductor
nanoparticles having an aspect ratio greater than 1.5 and different
from those used in step iii) for a contacting time of less than 15
minutes.
30. The process for the manufacture of an electro-luminescent film
according to claim 27, wherein the surface electric potential is
induced and maintained on the substrate during contact with
colloidal dispersion.
31. The process for the manufacture of an electro-luminescent film
according to claim 30, wherein the repetition unit of the pattern
comprises at least two pixels and wherein semiconductor
nanoparticles on the first pixel of the at least two pixels are
different from semiconductor nanoparticles on the second pixel of
the at least two pixels; and wherein process further comprises: iv)
drying the substrate and semiconductor nanoparticles deposited
thereon to form an intermediate structure; v) inducing a surface
electric potential on the intermediate structure according to the
pattern, so that the second pixel of the repetition unit is induced
in the whole pattern; and vi) bringing the electret substrate in
contact with a colloidal dispersion of semiconductor nanoparticles
having an aspect ratio greater than 1.5 and different from those
used in step iii) for a contacting time of less than 15 minutes;
while surface electric potential is maintained.
32. A light emitting device comprising an electro-luminescent film
comprising a substrate and semiconductor nanoparticles on the
substrate according to a periodic pattern, wherein semiconductor
nanoparticles have an aspect ratio greater than 1.5; wherein the
repetition unit of the pattern has a smallest dimension of less
than 500 micrometer and comprises at least one pixel.
Description
FIELD OF INVENTION
[0001] The present invention pertains to the field of
electro-luminescent materials. In particular, the invention relates
to an electro-luminescent film, a process to prepare an
electro-luminescent film and a light emitting device comprising an
electro-luminescent film.
BACKGROUND OF INVENTION
[0002] To represent colors in all their variety, one proceeds
typically by additive synthesis of at least three complementary
colors, especially red, green and blue. In a chromaticity diagram,
the subset of available colors obtained by mixing different
proportions of these three colors is formed by the triangle formed
by the three coordinates associated with the three colors red,
green and blue. This subset constitutes what is called a gamut.
[0003] A luminescent display device has to represent the widest
possible gamut for an accurate color reproduction. For this, the
composing sub-pixels must be of the most saturated colors possible.
A light source has a saturated color if it is close to a
monochromatic color. From a spectral point of view, this means that
light emitted by the source is comprised of a single luminescence
narrow band. A highly saturated shade has a vivid, intense color
while a less saturated shade appears rather bland and gray.
[0004] It is therefore important to have light sources whose
emission spectra are narrow and with saturated colors.
[0005] Semiconductor nanoparticles, commonly called "quantum dots",
are known as emissive material. Said objects have a narrow
luminescence spectrum, approximately 30 nm full width at half
maximum, and offer the possibility to tune their light emission in
the entire visible spectrum as well as in infrared range after
electric charges injection. Electrical current is forced into
semiconductor nanoparticles, which energy eventually relax by
emission of light.
[0006] Document US 2019/040,313 discloses fluorescent films
comprising composite particles encapsulating semiconductor
nanoplatelets in an inorganic material. Said films are not
electro-luminescent films; indeed, the encapsulation of
semiconductor nanoplatelets in a composite particle prevents the
direct electrons injection into the semiconductor nanoplatelets
because the encapsulating material acts as an insulator around the
nanoplatelets.
[0007] Document U.S. Pat. No. 9,975,764 discloses films comprising
latex particles deposited on an electret substrate. Said films are
not electro-luminescent films as latex particles are not suitable
for electrons injection.
[0008] It is known to use nanoplatelets to obtain great spectral
emission bandwidth and a perfect control of the emission wavelength
(see WO2013/140083).
[0009] However, distributing such semiconductor nanoparticles on a
periodic pattern with well controlled size, i.e. size of
nanoparticles deposit and/or size of pattern, is still an unmet
challenge. For example, inkjet printing is not suitable to obtain a
small repetition unit of a pattern (i.e. less than 500 micrometer)
and comprising at least one pixel. Moreover the ink-jet technique
is time consuming, considering that the deposition in general is
not parallelized and also the constraints about the viscosity and
nature of the used solvents are quite strong.
[0010] It is therefore an object of the present invention to
provide an electro-luminescent film having well controlled periodic
pattern, which can be used as elementary brick for various light
emitting devices, like display devices.
SUMMARY
[0011] This invention thus relates to an electro-luminescent film
comprising a substrate and semiconductor nanoparticles distributed
on the substrate according to a periodic pattern, wherein
semiconductor nanoparticles have an aspect ratio greater than 1.5;
wherein the repetition unit of the pattern has a smallest dimension
of less than 500 micrometer and comprises at least one pixel.
[0012] According to an embodiment, the pattern is periodic in two
dimensions, preferably the periodic pattern is a rectangular
lattice or a square lattice.
[0013] According to an embodiment, semiconductor nanoparticles are
inorganic, preferably semiconductor nanoparticles are semiconductor
nanocrystals comprising a material of formula
M.sub.xQ.sub.yE.sub.zA.sub.w, wherein: M is selected from the group
consisting of Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os,
Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba,
Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cs; Q is selected from the
group consisting of Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru,
Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr,
Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr,
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cs; E is selected from the
group consisting of O, S, Se, Te, C, N, P, As, Sb, F, Cl, Br, I; A
is selected from the group consisting of O, S, Se, Te, C, N, P, As,
Sb, F, Cl, Br, I; and x, y, z and w are independently a rational
number from 0 to 5; x, y, z and w are not simultaneously equal to
0; x and y are not simultaneously equal to 0; z and w are not
simultaneously equal to 0.
[0014] According to an embodiment, semiconductor nanoparticles have
a longest dimension greater than 25 nanometers, preferably greater
than 35 nm.
[0015] According to an embodiment, semiconductor nanoparticles are
on the substrate with their longest dimension substantially aligned
in a predetermined direction.
[0016] According to an embodiment, substrate is selected from a
conductive material and a semi-conductive material.
[0017] According to an embodiment, semiconductor nanoparticles on
the substrate form layers with a thickness of less than 100 nm.
[0018] According to an embodiment, the repetition unit of the
periodic pattern comprises at least two pixels, preferably,
semiconductor nanoparticles on the first pixel of the at least two
pixels are different from semiconductor nanoparticles on the second
pixel of the at least two pixels.
[0019] The invention also relates to a first process for the
manufacture of an electro-luminescent film comprising a substrate
and semiconductor nanoparticles distributed on the substrate
according to a periodic pattern, wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least one pixel comprising the steps of. [0020] i)
providing an electret substrate; [0021] ii) writing a surface
electric potential on the electret substrate according to the
pattern, so that at least one pixel of the repetition unit is
written in the whole pattern; and [0022] iii) bringing the electret
substrate in contact with a colloidal dispersion of semiconductor
nanoparticles having an aspect ratio greater than 1.5 for a
contacting time of less than 15 minutes.
[0023] The invention also relates to a second process for the
manufacture of an electro-luminescent film comprising a substrate
and semiconductor nanoparticles distributed on the substrate
according to a periodic pattern, wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least two pixels and wherein semiconductor
nanoparticles on the first pixel of the at least two pixels are
different from semiconductor nanoparticles on the second pixel of
the at least two pixels comprising the steps of. [0024] i)
providing an electret substrate; [0025] ii) writing a surface
electric potential on the electret substrate according to the
pattern, so that the first pixel of the repetition unit is written
in the whole pattern; [0026] iii) bringing the electret substrate
in contact with a colloidal dispersion of semiconductor
nanoparticles having an aspect ratio greater than 1.5 for a
contacting time of less than 15 minutes; [0027] iv) drying the
electret substrate and semiconductor nanoparticles deposited
thereon to form an intermediate structure; [0028] v) writing a
surface electric potential on the intermediate structure according
to the pattern, so that the second pixel of the repetition unit is
written in the whole pattern; and [0029] vi) bringing the electret
substrate in contact with a colloidal dispersion of semiconductor
nanoparticles an aspect ratio greater than 1.5 and different from
those used in step iii) for a contacting time of less than 15
minutes.
[0030] The invention also relates to a third process for the
manufacture of an electro-luminescent film comprising a substrate
and semiconductor nanoparticles distributed on the substrate
according to a periodic pattern, wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least one pixel comprising the steps of: [0031] i)
Providing a substrate; [0032] ii) Inducing a surface electric
potential on the substrate according to the pattern, so that at
least one pixel of the repetition unit is induced in the whole
pattern; and [0033] iii) Bringing the substrate in contact with a
colloidal dispersion of semiconductor nanoparticles having an
aspect ratio greater than 1.5 for a contacting time of less than 15
minutes, while surface electric potential is maintained.
[0034] The invention also relates to a fourth process for the
manufacture of an electro-luminescent film comprising a substrate
and semiconductor nanoparticles deposited on the substrate
according to a periodic pattern, wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least two pixels and wherein semiconductor
nanoparticles on the first pixel of the at least two pixels are
different from semiconductor nanoparticles on the second pixel of
the at least two pixels comprising the steps of: [0035] i)
Providing a substrate; [0036] ii) Inducing a surface electric
potential on the substrate according to the pattern, so that the
first pixel of the repetition unit is induced in the whole pattern;
[0037] iii) Bringing the substrate in contact with a colloidal
dispersion of semiconductor nanoparticles having an aspect ratio
greater than 1.5 for a contacting time of less than 15 minutes,
while surface electric potential is maintained; [0038] iv) Drying
the substrate and semiconductor nanoparticles deposited thereon to
form an intermediate structure; [0039] v) Inducing a surface
electric potential on the intermediate structure according to the
pattern, so that the second pixel of the repetition unit is induced
in the whole pattern; and [0040] vi) Bringing the substrate in
contact with a colloidal dispersion of semiconductor nanoparticles
having an aspect ratio greater than 1.5 and different from those
used in step iii) for a contacting time of less than 15 minutes,
while surface electric potential is maintained.
[0041] The invention further relates to a light emitting device
comprising an electro-luminescent film comprising a substrate and
semiconductor nanoparticles on the substrate according to a
periodic pattern, wherein semiconductor nanoparticles have an
aspect ratio greater than 1.5; wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least one pixel.
Definitions
[0042] In the present invention, the following terms have the
following meanings: [0043] "aspect ratio" is a feature of
anisotropic particles. An anisotropic particle has three
characteristic dimensions, one of which is the longest and one of
which is the shortest. Aspect ratio of an anisotropic particle is
the ratio of the longest dimension divided by the shortest
dimension. Aspect ratio is necessarily greater than 1. For
instance, a nanoparticle of length L=30 nm, width W=20 nm and
thickness T=10 nm has an aspect ratio of L/T=3, as shown on FIG. 2.
Shape factor is a synonym of aspect ratio. [0044] "blue range"
refers to the range of wavelength from 400 nm to 500 nm. [0045]
"colloidal" refers to a substance in which particles are dispersed,
suspended and do not settle, flocculate or aggregate; or would take
a very long time to settle appreciably, but are not soluble in said
substance. [0046] "colloidal nanoparticles" refers to nanoparticles
that may be dispersed, suspended and which would not settle,
flocculate or aggregate; or would take a very long time to settle
appreciably in another substance, typically in an aqueous or
organic solvent, and which are not soluble in said substance.
"Colloidal nanoparticles" does not refer to particles grown on
substrate. [0047] "core/shell" refers to heterogeneous
nanostructure comprising an inner part: the core, overcoated on its
surface, totally or partially, by a film or a layer of at least one
atom thick material different from the core: the shell. Core/shell
structures are noted as follows: core material/shell material. For
instance, a particle comprising a core of CdSe and a shell of ZnS
is noted CdSe/ZnS. By extension, core/shell/shell structures are
defined as core/first-shell structures overcoated on their surface,
totally or partially, by a film or a layer of at least one atom
thick material different from the core and/or from the first shell:
the second-shell. For instance, a particle comprising a core of
CdSe.sub.0.45S.sub.0.55, a first-shell of Cd.sub.0.80Zn.sub.0.20S
and a second-shell of ZnS is noted
CdSe.sub.0.45S.sub.0.55/Cd.sub.0.80Zn.sub.0.20S/ZnS. [0048]
"display device" refers to a device that displays an image signal.
Display devices include all devices that display an image such as,
non-limitatively, a television, a computer monitor, a personal
digital assistant, a mobile phone, a laptop computer, a tablet PC,
a tablet phone, a foldable tablet phone, an MP3 player, a CD
player, a DVD player, a Blu-Ray player, a projector, a head mounted
display, a smart watch, a watch phone or a smart device. [0049]
"electret" refers to a material able to have a non-zero
polarization density (i.e. the material contains electric dipole
moments) for a long time, without external electric field.
Polarization density may be created by injection of electric
charges in material, said charges creating polarization density. In
an electret material, dissipation of polarization density is slow
(as compared to conductive materials), typically from tens of
seconds to tens of minutes. To the purpose of the invention, the
stability of polarization should be bigger than 1 minute. [0050]
"electro-luminescent" refers to the property of a material that
emits light when electric current flows in the material. Actually,
electric current drives said material in an excited state, which
eventually relaxes by emission of light. [0051] "external quantum
efficiency" refers to the ratio of extracted photons over injected
carriers in a material. [0052] "FWHM" refers to Full Width at Half
Maximum for a band of emission/absorption of light. [0053] "green
range" refers to the range of wavelength from 500 nm to 600 nm.
[0054] "M.sub.xE.sub.z" refers to a material composed of chemical
element M and chemical element E, with a stoichiometry of x
elements of M for z elements of E, x and z being independently a
decimal number from 0 to 5; x and z not being simultaneously equal
to 0. The stoichiometry of M.sub.xE.sub.z is not strictly limited
to x:z but includes slight variations in composition due to
nanometric size of nanoparticles, crystalline face effect and
potentially doping. Actually, M.sub.xE.sub.z defines material with
M content in atomic composition between x-5% and x+5%; with E
content in atomic composition between z-5% and z+5%; and with
atomic composition of compounds different from M or E from 0.001%
to 5%. Same principle applies for materials composed of three of
four chemical elements. [0055] "nanoparticle" refers to a particle
having at least one dimension in the 0.1 to 100 nanometers range.
Nanoparticles may have any shape. A nanoparticle may be a single
particle or an aggregate of several single particles. Single
particles may be crystalline. Single particles may have a
core/shell or plate/crown structure. [0056] "nanoplatelet" refers
to a nanoparticle having a 2D-shape, i.e. having one dimension
smaller than the two others; said smaller dimension ranging from
0.1 to 100 nanometers. In the sense of the present invention, the
smallest dimension (hereafter referred to as the thickness) is
smaller than the other two dimensions (hereafter referred to as the
length and the width) by a factor (aspect ratio) of at least 1.5.
FIG. 3 shows various nanoplatelets. [0057] "periodic pattern"
refers to an organization of a surface on which a geometric element
is repeated regularly, the length of repetition being the period.
Lattices are specific periodic patterns. [0058] "pixel" refers to a
geometrical area in a repetition unit. By extension, if
nanoparticles are on said area and form a volume of material: this
volume is also a pixel. In particular, a pixel may be a sub-unit of
a repetition unit. [0059] "red range" refers to the range of
wavelength from 600 nm to 720 nm. [0060] "repetition unit" refers
to a single geometric element that is repeated in a periodic
pattern.
DETAILED DESCRIPTION
[0061] The following detailed description will be better understood
when read in conjunction with the drawings. For the purpose of
illustrating, the electro-luminescent film is shown in a preferred
embodiment. It should be understood, however that the application
is not limited to the precise arrangements, structures, features,
embodiments, and aspect shown. The drawings are not drawn to scale
and are not intended to limit the scope of the claims to the
embodiments depicted. Accordingly, it should be understood that
where features mentioned in the appended claims are followed by
reference signs, such signs are included solely for the purpose of
enhancing the intelligibility of the claims and are in no way
limiting on the scope of the claims.
[0062] This invention relates to an electro-luminescent film
comprising a substrate and semiconductor nanoparticles distributed
on the substrate according to a periodic pattern. The repetition
unit of the pattern has a smallest dimension of less than 500
micrometer.
[0063] In some embodiments, the smallest dimension of the
repetition unit of the pattern is less than 300 micrometer, less
than 200 micrometer, less than 100 micrometer, less than 80
micrometer, less than 50 micrometer, less than 40 micrometer, less
than 30 micrometer. Preferably, the smallest dimension of the
repetition unit is greater than 3 micrometer, preferably greater
than 5 micrometer, more preferably greater than 10 micrometer.
Indeed, repetition unit size should be large enough to avoid
diffraction or scattering of light emitted by semiconductor
nanoparticles.
[0064] The electro-luminescent film is illustrated in FIG. 1.
[0065] In the invention, the repetition unit of the periodic
pattern comprises at least one pixel. A pixel is actually a sub
unit of the repetition unit. Semiconductor nanoparticles are
localized on the area defined by said pixel. Consequently,
electro-luminescent film of the invention comprises deposits of
semiconductor nanoparticles distributed on a periodic pattern.
Preferably, the smallest dimension of the pixel is greater than 3
micrometer. Indeed, pixel size should be large enough to avoid
diffraction or scattering of light emitted by semiconductor
nanoparticles which constitute pixels.
[0066] In the invention, semiconductor nanoparticles are
anisotropic and have an aspect ratio greater than 1.5. In some
embodiments, semiconductor nanoparticles have an aspect ratio
greater than 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15,
20. Semiconductor nanoparticles may have an ovoid shape, a
discoidal shape, a cylindrical shape, a faceted shape, a hexagonal
shape, a triangular shape, or a platelet shape. Anisotropic
particles present the following advantage: along their smallest
dimension, they define a quantum effect which is not affected by
their longest dimension. With anisotropic particles, it is possible
to have one dimension of 1 to 1.2 nm yielding the quantum effect
expected in blue range and another dimension much longer, for
instance greater than 10 nm, allowing to manage stability of
particles and to tune optical properties of particles. Moreover,
controlling the size of only one dimension, i.e. thickness for
nanoplatelets, is easier than controlling sizes in three
dimensions, as it is required for spherical quantum dots. Last,
FWHM of emission spectra of semiconductor nanoplatelets is lower
than for quantum dots: emission bands are narrower, and the typical
photoluminescence decay time of semiconductor nanoplatelets is 1
order of magnitude faster than for spherical quantum dots.
[0067] Preferably, the semiconductor nanoparticles have a 1D shape
(cylindrical shape) or a 2D shape (platelet shape). Advantageously,
a 1D shape allows confinement of excitons in two dimensions and
allows free propagation in the other dimension, a 2D shape allows
confinement of excitons in one dimension and allows free
propagation in the other two dimensions, whereas a quantum dot (or
spherical nanocrystal) has a 3D shape and allow confinement of
excitons in all three spatial dimensions. These particular 2D and
1D confinements result in distinct electronic and optical
properties, for example a faster photoluminescence decay time and a
narrower optical feature with full width at half maximum (FWHM)
much lower than for spherical quantum dots.
[0068] It is worth noting that quantum dots and semiconductor
nanoplatelets are quite different regarding their optical
properties, but also regarding their morphology and their surface
chemistry: [0069] the organization of M and E atoms (for a formula
M.sub.xE.sub.z) at the surface of a nanoplatelet and at the surface
of a quantum dot are different; [0070] the organization of surface
ligands is thus also different; [0071] nanoplatelets have specific
exposed crystalline facets different from quantum dots; and [0072]
nanoplatelets have a higher specific surface than quantum dots
(this is valid for a nanoplatelet having a thickness R and a
quantum dot having the same diameter R, wherein lateral dimensions
of the nanoplatelet being superior to 5/3R).
[0073] According to an embodiment, the pattern is periodic in two
dimensions, preferably the periodic pattern is a rectangular
lattice or a square lattice. Such periodic patterns allow for easy
localization of each elementary unit on the electro-luminescent
film, which is desirable to address electrically each elementary
unit.
[0074] According to an embodiment, semiconductor nanoparticles are
inorganic, in particular, semiconductor nanoparticles may be
semiconductor nanocrystals comprising a material of formula
M.sub.xQ.sub.yE.sub.zA.sub.w (I)
[0075] wherein:
[0076] M is selected from the group consisting of Zn, Cd, Hg, Cu,
Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd,
Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb,
As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Cs;
[0077] Q is selected from the group consisting of Zn, Cd, Hg, Cu,
Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd,
Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb,
As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Cs;
[0078] E is selected from the group consisting of O, S, Se, Te, C,
N, P, As, Sb, F, Cl, Br, I;
[0079] A is selected from the group consisting of O, S, Se, Te, C,
N, P, As, Sb, F, Cl, Br, I; and
[0080] x, y, z and w are independently a decimal number from 0 to
5; x, y, z and w are not simultaneously equal to 0; x and y are not
simultaneously equal to 0; z and w may not be simultaneously equal
to 0. Preferably, semiconductor nanoparticles have one of their
dimensions lower than the Bohr radius of electron-hole pair in the
material.
[0081] Herein, the formulas M.sub.xQ.sub.yE.sub.zA.sub.w (I) and
M.sub.xN.sub.yE.sub.zA.sub.w can be used interchangeably (wherein Q
or N is selected from the group consisting of Zn, Cd, Hg, Cu, Ag,
Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta,
Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As,
Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Cs).
[0082] In one embodiment, semiconductor nanoparticles comprise a
semiconductor material selected from the group consisting of group
IV, group IIIA-VA, group IIA-VIA, group IIIA-VIA, group
IA-IIIA-VIA, group IIA-VA, group IVA-VIA, group VIB-VIA, group
VB-VIA, group IVB-VIA or mixture thereof.
[0083] In a specific configuration of this embodiment,
semiconductor nanocrystals have a homostructure. By homostructure,
it is meant that each particle is homogenous and has the same local
composition in all its volume. In other words, each particle is a
core particle without a shell.
[0084] In a specific configuration of this embodiment,
semiconductor nanocrystals have a core/shell structure. The core
comprises a material of formula M.sub.xQ.sub.yE.sub.zA.sub.w as
defined above. The shell comprises a material different from core
of formula M.sub.xQ.sub.yE.sub.zA.sub.w as defined above, such as a
material of formula
M'.sub.x'Q'.sub.y'E'.sub.z'A'.sub.w' (II)
[0085] wherein:
[0086] M' is selected from the group consisting of Zn, Cd, Hg, Cu,
Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd,
Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb,
As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Cs;
[0087] Q' is selected from the group consisting of Zn, Cd, Hg, Cu,
Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd,
Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb,
As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Cs;
[0088] E' is selected from the group consisting of O, S, Se, Te, C,
N, P, As, Sb, F, Cl, Br, I;
[0089] A' is selected from the group consisting of O, S, Se, Te, C,
N, P, As, Sb, F, Cl, Br, I; and
[0090] x', y', z' and w are independently a decimal number from 0
to 5; x', y', z' and w' are not simultaneously equal to 0; x' and
y' are not simultaneously equal to 0; z' and w' may not be
simultaneously equal to 0.
[0091] In a more specific configuration of this embodiment,
semiconductor nanocrystals have a core/first-shell/second-shell
structure (i.e. core/shell/shell structure). The core comprises a
material of formula M.sub.xQ.sub.yE.sub.zA.sub.w as defined above.
The first-shell comprises a material different from core of formula
M.sub.xQ.sub.yE.sub.zA.sub.w as defined above. The second-shell is
deposited partially or totally on the first-shell with the same
features, or different features than the first-shell, such as for
example same or different thickness. The material of second-shell
is different from the material of the first shell and/or of the
material of the core. By analogy, structures with three or four
shells may be prepared.
[0092] In a specific configuration of this embodiment,
semiconductor nanocrystals have a core/crown structure. The
embodiments concerning shells apply mutatis mutandis to crowns in
terms of composition, thickness, properties, number of layers of
material.
[0093] In a configuration of this embodiment, semiconductor
nanoparticles are colloidal nanoparticles.
[0094] In a configuration of this embodiment, semiconductor
nanoparticles are electrically neutral. With electrically neutral
semiconductor nanoparticles, it is easier to manage deposition on
substrate, especially when deposition is driven by electrical
polarization.
[0095] In a specific configuration of this embodiment,
semiconductor nanoparticles emit red light when stimulated
electrically. Emitted red light is typically a band centered on a
wavelength shorter than 720 nm and longer than 600 nm, preferably
shorter than 670 nm and longer than 620 nm, more preferably shorter
than 635 nm and longer than 625 nm. Emitted red light is typically
a band having a FWHM less than 50 nm, preferably less than 30 nm,
more preferably less than 20 nm, i.e. a FWHM less than 0.16 eV,
preferably less than 0.096 eV, more preferably less than 0.064
eV.
[0096] In a specific configuration of this embodiment,
semiconductor nanoparticles emit green light when stimulated
electrically. Emitted green light is typically a band centered on a
wavelength shorter than 600 nm and longer than 500 nm, preferably
shorter than 550 nm and longer than 520 nm, more preferably shorter
than 535 nm and longer than 525 nm. Emitted green light is
typically a band having a FWHM less than 50 nm, preferably less
than 30 nm, more preferably less than 20 nm, i.e. FWHM less than
0.22 eV, preferably less than 0.13 eV, more preferably less than
0.08 eV.
[0097] In a specific configuration of this embodiment,
semiconductor nanoparticles emit blue light when stimulated
electrically. Emitted blue light is typically a band centered on a
wavelength shorter than 500 nm and longer than 400 nm, preferably
shorter than 480 nm and longer than 420 nm, more preferably shorter
than 455 nm and longer than 435 nm. Emitted blue light is typically
a band having a FWHM less than 50 nm, preferably less than 30 nm,
more preferably less than 20 nm, i.e. a FWHM less than 0.306 eV,
preferably less than 0.184 eV, more preferably less than 0.122
eV.
[0098] In a configuration of this embodiment, semiconductor
nanoparticles are selected from CdSe.sub.xS.sub.(1-x)/CdS/ZnS,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S,
CdSe.sub.xS.sub.(1-x)/ZnS,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdSe.sub.xS.sub.(1-x)/CdS, CdSe/CdS/ZnS, CdSe/CdS,
CdSe/Cd.sub.yZn.sub.(1-y)S, CdSe/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdSe.sub.xS.sub.(1-x)/CdS/ZnSe,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se,
CdSe.sub.xS.sub.(1-x)/ZnSe,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se/ZnSe,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se/ZnS, CdSe/CdS/ZnSe,
CdSe/Cd.sub.yZn.sub.(1-y)Se, CdSe/Cd.sub.yZn.sub.(1-y)Se/ZnSe
CdSe/Cd.sub.yZn.sub.(1-y)Se/ZnS,
CdSe.sub.xS.sub.(1-x)/CdS/ZnSe.sub.yS.sub.(1-y),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S,
CdSe.sub.xS.sub.(1-x)/ZnSe.sub.yS.sub.(1-y),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/CdS, CdSe/CdS/ZnSe.sub.yS.sub.(1-y),
CdSe/CdS, CdSe/Cd.sub.yZn.sub.(1-y)S,
CdSe/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/CdS/ZnSe.sub.yS.sub.(1-y),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se,
CdSe.sub.xS.sub.(1-x)/ZnSe.sub.yS.sub.(1-y),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se/ZnSe.sub.zS.sub.(1-z),
CdSe/Cd.sub.yZn.sub.(1-y)Se,
CdSe/Cd.sub.yZn.sub.(1-y)Se/ZnSe.sub.zS.sub.(1-z),
CdSe/Cd.sub.yZn.sub.(1-y)Se/ZnSe.sub.zS.sub.(1-z) where x, y and z
are rational numbers between 0 (excluded) and 1 (excluded), and
emit red light when stimulated electrically. Emitted red light is
typically a band centered on a wavelength shorter than 720 nm and
longer than 600 nm, preferably shorter than 670 nm and longer than
620 nm, more preferably shorter than 635 nm and longer than 625 nm.
Emitted red light is typically a band having a FWHM less than 50
nm, preferably less than 30 nm, more preferably less than 20 nm.
Suitable semiconductor nanoparticles emitting red light at 630 nm
are core/shell/shell nanoplatelets of
CdSe.sub.0.45S.sub.0.55/Cd.sub.0.30Zn.sub.0.70S/ZnS, with a core of
thickness 1.2 nm and a lateral dimension, i.e. length or width,
greater than 8 nm and shells of thicknesses 2.5 nm and 2 nm. Other
suitable semiconductor nanoparticles emitting red light at 630 nm
are core/shell/shell nanoplatelets of
CdSe.sub.0.65S.sub.0.35/CdS/ZnS, with a core of thickness 1.2 nm
and a lateral dimension, i.e. length or width, greater than 8 nm
and shells of thicknesses 2.5 nm and 2 nm.
[0099] In a configuration of this embodiment, semiconductor
nanoparticles are selected from CdSe.sub.xS.sub.(1-x)/CdS/ZnS,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S,
CdSe.sub.xS.sub.(1-x)/ZnS,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdSe.sub.xS.sub.(1-x)/CdS, CdSe/CdS/ZnS, CdSe/CdS,
CdSe/Cd.sub.yZn.sub.(1-y)S, CdSe/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdSe.sub.xS.sub.(1-x)/CdS/ZnSe,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se,
CdSe.sub.xS.sub.(1-x)/ZnSe,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se/ZnSe,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se/ZnS, CdSe/CdS/ZnSe,
CdSe/Cd.sub.yZn.sub.(1-y)Se, CdSe/Cd.sub.yZn.sub.(1-y)Se/ZnSe
CdSe/Cd.sub.yZn.sub.(1-y)Se/ZnS, CdS/ZnSe,
CdSe.sub.xS.sub.(1-x)/ZnS/Cd.sub.yZn.sub.(1-y)S/ZnS, CdS/ZnS,
CdS/Cd.sub.yZn.sub.(1-y)S, CdS/Cd.sub.yZn.sub.(1-y)S/ZnS, CdS/ZnSe,
CdS/Cd.sub.yZn.sub.(1-y)Se, CdS/ZnSe,
CdS/Cd.sub.yZn.sub.(1-y)Se/ZnSe, CdS/Cd.sub.yZn.sub.(1-y)Se/ZnS,
CdS/ZnSe, CdS/ZnS/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdSe.sub.xS.sub.(1-x)/CdS/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S,
CdSe.sub.xS.sub.(1-x)/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/CdS,
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se,
CdSe.sub.xS.sub.(1-x)/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/Cd.sub.yZn.sub.(1-y)Se/ZnSe.sub.zS.sub.(1-z),
CdS/ZnSe.sub.zS.sub.(1-z),
CdSe.sub.xS.sub.(1-x)/ZnSe.sub.zS.sub.(1-z)/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdSe.sub.xS.sub.(1-x)/ZnSe.sub.zS.sub.(1-z)/Cd.sub.yZn.sub.(1-y)S/ZnSe.su-
b.zS.sub.(1-z), CdS/Cd.sub.yZn.sub.(1-y)S,
CdS/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
CdS/Cd.sub.yZn.sub.(1-y)Se, CdS/ZnSe.sub.zS.sub.(1-z),
CdS/ZnSe.sub.zS.sub.(1-z)/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdS/ZnSe.sub.zS.sub.(1-z)/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
CdS/ZnS/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
Cd.sub.yZn.sub.(1-y)Se/ZnSe/ZnSe.sub.zS.sub.(1-z)/ZnS where x, y
and z are rational numbers between 0 (excluded) and 1 (excluded),
and emit green light when stimulated electrically. Emitted green
light is typically a band centered on a wavelength shorter than 600
nm and longer than 500 nm, preferably shorter than 550 nm and
longer than 520 nm, more preferably shorter than 535 nm and longer
than 525 nm. Emitted green light is typically a band having a FWHM
less than 50 nm, preferably less than 30 nm, more preferably less
than 20 nm. Suitable semiconductor nanoparticles emitting green
light at 530 nm are core/shell/shell nanoplatelets of
CdSe.sub.0.10S.sub.0.90/ZnS/Cd.sub.0.20Zn.sub.0.80S, with a core of
thickness 1.5 nm and a lateral dimension, i.e. length or width,
greater than 10 nm and shells of thicknesses 1 nm and 2.5 nm. Other
suitable semiconductor nanoparticles emitting green light at 530 nm
are core/shell/shell nanoplatelets of
CdSe.sub.0.20S.sub.0.80/ZnS/Cd.sub.0.15Zn.sub.0.85S, with a core of
thickness 1.2 nm and a lateral dimension, i.e. length or width,
greater than 10 nm and shells of thicknesses 1 nm and 2.5 nm.
[0100] In a configuration of this embodiment, semiconductor
nanoparticles are selected from CdS/ZnSe, CdS/ZnS,
CdS/Cd.sub.yZn.sub.(1-y)S, CdS/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdS/Cd.sub.yZn.sub.(1-y)Se, CdS/Cd.sub.yZn.sub.(1-y)Se/ZnSe,
CdS/Cd.sub.yZn.sub.(1-y)Se/ZnS, CdS/ZnS/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdS/ZnSe.sub.zS.sub.(1-z), CdS/Cd.sub.yZn.sub.(1-y)S,
CdS/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
CdS/Cd.sub.yZn.sub.(1-y)Se, CdS/ZnSe.sub.zS.sub.(1-z),
CdS/ZnSe.sub.zS.sub.(1-z)/Cd.sub.yZn.sub.(1-y)S/ZnS,
CdS/ZnSe.sub.zS.sub.(1-z)/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z),
CdS/ZnS/Cd.sub.yZn.sub.(1-y)S/ZnSe.sub.zS.sub.(1-z), where x, y and
z are rational numbers between 0 (excluded) and 1 (excluded), and
emit blue light when stimulated electrically. Emitted blue light is
typically a band centered on a wavelength shorter than 500 nm and
longer than 400 nm, preferably shorter than 480 nm and longer than
420 nm, more preferably shorter than 455 nm and longer than 435 nm.
Emitted blue light is typically a band having a FWHM less than 50
nm, preferably less than 30 nm, more preferably less than 20 nm.
Suitable semiconductor nanoparticles emitting blue light at 450 nm
are core/shell nanoplatelets of CdS/ZnS, with a core of thickness
0.9 nm and a lateral dimension, i.e. length or width, greater than
15 nm and a shell of thickness 1 nm.
[0101] In another embodiment, semiconductor nanoparticles have a
longest dimension greater than 25 nm, preferably greater than 35
nm, more preferably greater than 50 nm. Actually, the association
of anisotropy and a size larger than 25 nm along the longest
dimension is favorable for deposition of semiconductor
nanoparticles on substrate, in particular under di-electrophoretic
conditions. It has been observed that larger particles are
deposited quicker than smaller one. Besides, under
di-electrophoretic conditions electro-rotation phenomenon takes
place and leads to deposition in an oriented manner. In the
specific configuration in which semiconductor nanoparticles are
nanoplatelets deposited in an oriented manner and having their
smallest face on the substrate, light emitted by the semiconductor
nanoparticles is linearly polarized in a direction perpendicular to
direction of orientation of the semiconductor nanoparticles. This
is particularly advantageous in devices like display in which
polarizing filters are used.
[0102] In another embodiment, semiconductor nanoparticles are on
the substrate with their longest dimension substantially aligned in
a predetermined direction. Such orientation of semiconductor
nanoparticles allows for compact deposition, which has three
advantages. First, thickness of deposit is reduced for a same
quantity of semiconductor nanoparticles deposited and a thin
electro-luminescent film is desirable for manufacturing reasons.
Second, compact deposit enhances electric contact between
semiconductor nanoparticles, such contacts being crucial to inject
electricity in all semiconductor nanoparticles. Indeed, with a
compact deposit, one can expect an improved yield of light emission
for a same amount of electricity injected in semiconductor
nanoparticles. Last, a good vertical stacking and assembly of
semiconductor nanoparticles permit a better control of the
thickness of the electro-luminescent layer. In this embodiment,
"substantially aligned in a predetermined direction" means that at
least X=50% of the nanoparticles are aligned in a predetermined
direction, preferably at least 60% of the nanoparticles are aligned
in a predetermined direction, more preferably at least 70% of the
nanoparticles are aligned in a predetermined direction, most
preferably at least 90% of the nanoparticles are aligned in a
predetermined direction.
[0103] In another embodiment, substrate is selected from a
conductive material and a semi-conductive material, preferably in
the form of a layer of conductive material and a semi-conductive
material. Indeed, substrate must enable electric current injection
into semiconductor nanoparticles that are on substrate. Said
conductive or semi-conductive layer is preferably under the form of
a network enabling electric injection of current in each repetition
unit independently, and preferably in each pixel of each repetition
unit independently.
[0104] Conductive or semi-conductive material may be selected from
Indium Tin Oxide (ITO), Aluminum doped Zinc Oxide (AZO), Fluorine
doped Zinc Oxide (FZO), Graphene or other allotropic forms of
carbon, Silver nanowires meshes, Silicon, Silicon on Insulator
(SOI), Germanium on Insulator (GOI), Silicon-Germanium on insulator
(SGOI), Doped Silicon substrates. It's worth noting that limit
between conductive and semi-conductive materials is sometimes
difficult to define, in particular with doped materials whose
conductive properties are dependent upon doping concentration.
[0105] A specific embodiment of semi-conductive substrate is a
conductive substrate on which a very thin layer of non-conductive,
i.e. insulating material is located. Preferably, this very thin
layer of non-conductive material is an electret material. The
non-conductive layer is thin enough to allow for electric current
injection through said non-conductive layer. Acceptable thickness
for said non-conductive layer depends on insulating material, but
is preferably less than 200 nm.
[0106] Suitable electret material may be selected from polymers,
for example: Fluorinated Ethylene Propylene (FEP),
Polytetrafluoroethylene (PTFE), Polyethylene (PE), Polycarbonate
(PC), Polypropylene (PP), Poly Vinylchloride (PVC), Polyethylene
Terephtalate (PET), Polyimide (PI), Polymethyl Methacrylate (PMMA),
Polyvinyl fluoride (PVF), Polyvinylidene Fluoride (PVDF),
Polydimethylsiloxane (PDMS), Ethylene Vinyl Acetate (EVA), Cyclic
Olefin Copolymers (COC), Polyparaxylylene (PPX), Fluorinated
parylenes and fluorinated polymers in amorphous form.
[0107] Other suitable electret materials may be selected from
inorganic materials, for example: Silicon Oxide (SiO.sub.2),
Silicon Nitride (Si.sub.3N.sub.4), Aluminium oxide
(Al.sub.2O.sub.3) or other doped mineral glass with known dopant
atoms (as example Na, S, Se, B).
[0108] For instance, a layer of Silicon, optionally doped, with a
thin layer of 100 nm of polymethylmethacrylate polymer (PMMA) is
suitable as substrate.
[0109] In another embodiment, substrate is a soft material, for
instance a non-conductive polymeric material, preferably an
electret material, configured to be transferred on a
semi-conductive or conductive support. By transferred, it is meant
any method yielding a structure comprising said soft material on
the semi-conductive or conductive support. Transfer may be direct,
without any material between substrate and support: this is a
direct contact between the substrate and the support. Transfer may
use an adhesive between substrate and support, preferably a
conductive adhesive. Transfer may use an intermediate carrier. This
embodiment enables production of large pieces of substrate which
may be stored for some time before being cut on demand and reported
on semi-conductive or conductive supports.
[0110] In another embodiment, semiconductor nanoparticles on the
substrate form layers with a thickness of less than 100 nm.
Preferably, the thickness is ranging between 10 nm and 50 nm.
Indeed, low thicknesses are preferred to design electronic devices,
in particular for electro-luminescent devices where too long
charges path could enhance non-radiative recombination. Moreover,
too thick optical layers could enhance undesired optical
reabsorption of emitted light.
[0111] In another embodiment, the volume fraction of semiconductor
nanoparticles deposed on a pixel is ranging from 10% to 90%,
preferably from 20% to 90%, more preferably from 30% to 90%, most
preferably from 50% to 90%.
[0112] In another embodiment, a pixel comprises a density of
semiconductor nanoparticles per surface unit greater than
5.times.10.sup.9 nanoparticles.cm.sup.-2, preferably greater than
7.times.10.sup.9 nanoparticles.cm.sup.-2, more preferably greater
than 5.times.10.sup.10 nanoparticles.cm.sup.-2, most preferably
greater than 5.times.10.sup.11 nanoparticles.cm.sup.-2. The density
of semiconductor nanoparticles per surface unit in a pixel refers
to the number of semiconductor nanoparticles per volume unit in a
pixel multiplied by the thickness of the layer of semiconductor
nanoparticles on said pixel. A high density of semiconductor
nanoparticles is preferred because it allows a close contact
between semiconductor nanoparticles which is essential in the
electro-luminescent film. A high density of semiconductor
nanoparticles is preferred also because the film is more uniform,
compact and without cracks. A high density of semiconductor
nanoparticles is also preferred as it allows a high EQE (External
Quantum Efficiency), in particular an EQE higher than 5%,
preferably higher than 10%, more preferably higher than 20%.
[0113] In another embodiment, a pixel comprises at least
3.times.10.sup.14 nanoparticles.cm.sup.-3, preferably at least
5.times.10.sup.14 nanoparticles.cm.sup.-3, more preferably at least
5.times.10.sup.15 nanoparticles.cm.sup.-3, most preferably at least
1.times.10.sup.17 nanoparticles.cm.sup.-3.
[0114] In another embodiment, the repetition unit of the periodic
pattern comprises at least two pixels. In particular, semiconductor
nanoparticles on the first pixel of the at least two pixels are
different from semiconductor nanoparticles on the second pixel of
the at least two pixels. With such a configuration, the
electro-luminescent film emits two different lights allowing for
dichromatic device. In a preferred embodiment, the periodic pattern
comprises three pixels comprising each one type of semiconductor
nanoparticles, said three types of semiconductor nanoparticles
being different. In particular, a first pixel comprising
semiconductor nanoparticles with light emission in blue range, a
second pixel comprising semiconductor nanoparticles with light
emission in green range and a third pixel comprising semiconductor
nanoparticles with light emission in red range is preferred.
[0115] The invention aims also at manufacturing electro-luminescent
films. In order to deposit semiconductor nanoparticles on
substrate, di-electrophoretic forces may be used. Said forces
result in attraction of a polarizable object placed in an electric
field produced by an electrically polarized surface. In addition,
precision of deposition, i.e. definition of limits between areas
where semiconductor nanoparticles are deposited and areas where no
deposition occurs, is improved.
[0116] Semiconductor nanoparticles of the invention are
polarizable. Preferably, semiconductor nanoparticles are neutral,
i.e. not charged with permanent electric charges. In particular,
anisotropic semiconducting nanoparticles are subject to strong
di-electrophoretic forces considering that the physical dependence
is proportional to the third power of the bigger dimension of the
nanoparticles. Quantum Dots are limited in size by the emission
wavelength, but Quantum Plates could be synthetized with longer
dimensions (width and length) respect to the thickness (which
controls the emission wavelength).
[0117] Therefore, invention also relates to a process for the
manufacture of an electro-luminescent film comprising a substrate
and semiconductor nanoparticles distributed on the substrate
according to a periodic pattern, wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least one pixel comprising the steps of: [0118] i)
Providing a substrate; [0119] ii) Creating a surface electric
potential on the substrate according to the pattern, so that at
least one pixel of the repetition unit is created in the whole
pattern; and [0120] iii) Bringing the substrate in contact with a
colloidal dispersion of semiconductor nanoparticles having an
aspect ratio greater than 1.5 for a contacting time of less than 15
minutes.
[0121] During semiconductor nanoparticles deposition, substrate
needs to be electrically polarized. This polarization may be
permanent or induced.
[0122] Permanent polarization exists in materials known as
electret: after application of an electric field to an electret
material, a permanent electrical polarization remains. With
electret material, it is possible to write a surface electric
potential then to deposit semiconductor nanoparticles.
[0123] In this embodiment, the invention relates to a process for
the manufacture of an electro-luminescent film comprising a
substrate and semiconductor nanoparticles distributed on the
substrate according to a periodic pattern, wherein the repetition
unit of the pattern has a smallest dimension of less than 500
micrometer and comprises at least one pixel comprising the
following steps.
[0124] In a first step, providing an electret substrate. The
substrate may be any embodiment of substrate as defined above in
the detailed description of the electro-luminescent film of the
invention. A preferred substrate has an external layer of PMMA,
i.e. the substrate is PMMA or the substrate is a conductive or
semi-conductive material under a layer of PMMA.
[0125] In a second step, writing a surface electric potential on
the electret substrate according to the pattern, so that at least
one pixel of the repetition unit is written in the whole
pattern.
[0126] Then, in a third step, the electret substrate is brought in
contact with a colloidal dispersion of semiconductor nanoparticles
having an aspect ratio greater than 1.5 for a contacting time of
less than 15 minutes. Due to electric polarization density of
electret, a di-electrophoretic force is imposed to semiconductor
nanoparticles which are thus attracted towards the surface. As
semiconductor nanoparticles are anisotropic, an electro-rotation
effect takes place, yielding an improved deposition of
semiconductor nanoparticles: deposit is denser, eventually
semiconductor nanoparticles are oriented on the surface along a
predetermined direction.
[0127] Contact may be done by immersion of electret substrate in a
colloidal dispersion of semiconductor nanoparticles, preferably in
a colloidal dispersion comprising semiconductor nanoparticles in an
organic solvent, more preferably in a hydrocarbon solvent such as
cyclohexane, hexane, heptane, decane or pentane.
[0128] Alternatively, contact may be done by drop-casting, spin
coating, pouring a colloidal dispersion of semiconductor
nanoparticles on the substrate, or by micro-fluidic contact
system.
[0129] Alternatively, contact may be done by spraying micrometric
droplets of colloidal dispersion of semiconductor nanoparticles in
a flux of gas. Due to electric polarization density of electret, a
di-electrophoretic force is imposed to semiconductor nanoparticles.
It's worth noting that the solvent is preferably selected in
non-polar solvent (such as for example heptane, pentane, hexane,
decane), so that no di-electrophoretic forces are imposed to
solvent and, moreover, electrical forces are reduced when the
dielectric constant of the solvent is big, as in polar solvents.
Micrometric droplets are thus attracted towards the surface. At the
same time, drying occurs by evaporation of the solvent. As
micrometric droplets are bigger than single semiconductor
nanoparticles, the di-electrophoretic force effect is strongly
increased yielding an improved deposition of semiconductor
nanoparticles. This method enables coating of large surfaces of
substrate and improves homogeneity and speed of deposition.
Moreover, with a suitable calibration of the flow rate of the gas,
a strong reduction of nanoparticle solution waste and reduction of
cleaning processes are obtained.
[0130] All features of the electro-luminescent film of the
invention, in particular of semiconductor nanoparticles may be
implemented in said process.
[0131] In a variant of this embodiment, the invention also relates
to a process for the manufacture of an electro-luminescent film
comprising a substrate and semiconductor nanoparticles deposited on
the substrate according to a periodic pattern, wherein the
repetition unit of the pattern has a smallest dimension of less
than 500 micrometer and comprises at least two pixels and wherein
semiconductor nanoparticles on the first pixel of the at least two
pixels are different from semiconductor nanoparticles on the second
pixel of the at least two pixels comprising the following
steps.
[0132] In a first step, providing an electret substrate. The
substrate may be any embodiment of substrate as defined above in
the detailed description of the electro-luminescent film of the
invention. A preferred substrate has an external layer of PMMA,
i.e. the substrate is PMMA or the substrate is a conductive or
semi-conductive material under a layer of PMMA.
[0133] In a second step, writing a surface electric potential on
the electret substrate according to the pattern, so that the first
pixel of the repetition unit is written in the whole pattern.
[0134] In a third step, the electret substrate is brought in
contact with a colloidal dispersion of semiconductor nanoparticles
having an aspect ratio greater than 1.5 for a contacting time of
less than 15 minutes.
[0135] Then, in a fourth step, electret substrate and semiconductor
nanoparticles deposited thereon are dried to form an intermediate
structure. Said intermediate structure can be treated as an
electret substrate in the same manner as above if substrate surface
has not been totally covered with semiconductor nanoparticles, i.e.
if some surface of the electret substrate is still available to be
electrically influenced, said surface is thus available for
nanoparticles deposition.
[0136] In a fifth step, writing a surface electric potential on the
intermediate structure according to the pattern, so that the second
pixel of the repetition unit is written in the whole pattern.
[0137] The surface electric potential is written on parts of the
surface on which no nanoparticles have been deposited during steps
two to four.
[0138] In a sixth step, the electret substrate is brought in
contact with a colloidal dispersion of semiconductor nanoparticles
an aspect ratio greater than 1.5 and different from those used in
third step for a contacting time of less than 15 minutes.
[0139] In some embodiments, steps four to six may be reiterated to
yield a third pixel, a fourth pixel, without other limit than the
definition of the repetition unit and pixels.
[0140] In steps three and six, contact may be done by immersion of
electret substrate in a colloidal dispersion of semiconductor
nanoparticles or by spraying micrometric droplets as described
above.
[0141] Alternatively, contact may be done by drop-casting, spin
coating, pouring a colloidal dispersion of semiconductor
nanoparticles on the substrate, or by micro-fluidic contact
system.
[0142] All features of the electro-luminescent film of the
invention, in particular of semiconductor nanoparticles may be
implemented in said process.
[0143] Besides processes using electret substrate having a
permanent polarization, other processes use induced
polarization.
[0144] Induced polarization corresponds to materials in which
electrical polarization results from application of an external
electrical field. As soon as external field is removed, electrical
polarization disappears. In this case, it is possible to induce a
surface electric potential and deposit semiconductor nanoparticles
while surface electric potential is maintained.
[0145] In this embodiment, the invention relates to a process for
the manufacture of an electro-luminescent film comprising a
substrate and semiconductor nanoparticles distributed on the
substrate according to a periodic pattern, wherein the repetition
unit of the pattern has a smallest dimension of less than 500
micrometer and comprises at least one pixel comprising the
following steps.
[0146] In a first step, providing a substrate. The substrate may be
any embodiment of substrate as defined above in the detailed
description of the electro-luminescent film of the invention.
[0147] In a second step, inducing a surface electric potential on
the substrate according to the pattern, so that at least one pixel
of the repetition unit is induced in the whole pattern.
[0148] Then, in a third step, the substrate is brought in contact
with a colloidal dispersion of semiconductor nanoparticles having
an aspect ratio greater than 1.5 for a contacting time of less than
15 minutes, while surface electric potential is maintained. Due to
electric polarization density of substrate, a di-electrophoretic
force is imposed to semiconductor nanoparticles which are thus
attracted towards the surface. As semiconductor nanoparticles are
anisotropic, an electro-rotation effect takes place, yielding an
improved deposition of semiconductor nanoparticles: deposit is
denser, eventually semiconductor nanoparticles are oriented on the
surface along a predetermined direction.
[0149] Contact may be done by immersion of substrate in a colloidal
dispersion of semiconductor nanoparticles, preferably in a
colloidal dispersion comprising semiconductor nanoparticles in an
organic solvent, more preferably in a hydrocarbon solvent such as
cyclohexane, hexane, heptane or pentane.
[0150] Alternatively, contact may be done by drop-casting, spin
coating, pouring a colloidal dispersion of semiconductor
nanoparticles on the substrate, or by micro-fluidic contact
system.
[0151] Alternatively, contact may be done by spraying micrometric
droplets of colloidal dispersion of semiconductor nanoparticles in
a flux of gas. Due to electric polarization density of substrate, a
di-electrophoretic force is imposed to semiconductor nanoparticles.
It's worth noting that the solvent is preferably selected in
non-polar solvent, so that no di-electrophoretic forces are imposed
to solvent. Micrometric droplets are thus attracted towards the
surface. At the same time, drying occurs by evaporation of the
solvent. As micrometric droplets are bigger than single
semiconductor nanoparticles, the di-electrophoretic force effect is
strongly increased yielding an improved deposition of semiconductor
nanoparticles. This method enables coating of large surfaces of
substrate and improves homogeneity and speed of deposition.
Moreover, with a suitable calibration of the flow rate of the gas,
a strong reduction of nanoparticle solution waste and reduction of
cleaning processes are obtained.
[0152] During third step, one has to simultaneously maintain
surface electric potential and bring in contact the substrate with
the colloidal suspension. The device used to induce surface
electric potential may be located on side of the substrate on which
semiconductor nanoparticles are deposited. Alternatively, the
device used to induce surface electric potential may be located on
the opposite side of the substrate's side on which semiconductor
nanoparticles are deposited. This second configuration is preferred
as contact between colloidal suspension and device used to induce
surface electric potential is avoided. However, this configuration
requires that substrate is not too thick: a thickness less than 50
.mu.m, preferably less than 20 .mu.m is preferred and allow
improved precision of deposition.
[0153] All features of the electro-luminescent film of the
invention, in particular of semiconductor nanoparticles may be
implemented in said process.
[0154] In a variant of this embodiment, the invention also relates
to a process for the manufacture of an electro-luminescent film
comprising a substrate and semiconductor nanoparticles deposited on
the substrate according to a periodic pattern, wherein the
repetition unit of the pattern has a smallest dimension of less
than 500 micrometer and comprises at least two pixels and wherein
semiconductor nanoparticles on the first pixel of the at least two
pixels are different from semiconductor nanoparticles on the second
pixel of the at least two pixels comprising the following
steps.
[0155] In a first step, providing a substrate. The substrate may be
any embodiment of substrate as defined above in the detailed
description of the electro-luminescent film of the invention.
[0156] In a second step, inducing a surface electric potential on
the substrate according to the pattern, so that the first pixel of
the repetition unit is induced in the whole pattern.
[0157] In a third step, the substrate is brought in contact with a
colloidal dispersion of semiconductor nanoparticles having an
aspect ratio greater than 1.5 for a contacting time of less than 15
minutes, while surface electric potential is maintained.
[0158] Then, in a fourth step, substrate and semiconductor
nanoparticles deposited thereon are dried to form an intermediate
structure. Said intermediate structure can be treated as a
substrate in the same manner as above if substrate surface has not
been totally covered with semiconductor nanoparticles, i.e. if some
surface of the substrate is still available to be electrically
influenced, said surface is thus available for nanoparticles
deposition.
[0159] In a fifth step, inducing a surface electric potential on
the intermediate structure according to the pattern, so that the
second pixel of the repetition unit is induced in the whole
pattern. The surface electric potential is induced on parts of the
surface on which no nanoparticles have been deposited during steps
two to four.
[0160] In a sixth step, the substrate is brought in contact with a
colloidal dispersion of semiconductor nanoparticles an aspect ratio
greater than 1.5 and different from those used in third step for a
contacting time of less than 15 minutes, while surface electric
potential is maintained.
[0161] During third and sixth steps, one has to simultaneously
maintain surface electric potential and bring in contact substrate
with colloidal suspension. The device used to induce surface
electric potential may be located on side of the substrate on which
semiconductor nanoparticles are deposited. Alternatively, the
device used to induce surface electric potential may be located on
the opposite side of the substrate's side on which semiconductor
nanoparticles are deposited. This second configuration is preferred
as contact between colloidal suspension and device used to induce
surface electric potential is avoided. However, this configuration
requires that substrate is not too thick: a thickness less than 50
.mu.m, preferably less than 20 .mu.m is preferred and allow
improved precision of deposition.
[0162] In some embodiments, steps four to six may be reiterated to
yield a third pixel, a fourth pixel, without other limit than the
definition of the repetition unit and pixels.
[0163] In steps three and six, contact may be done by immersion of
substrate in a colloidal dispersion of semiconductor nanoparticles
or by spraying micrometric droplets as described above.
[0164] All features of the electro-luminescent film of the
invention, in particular of semiconductor nanoparticles may be
implemented in said process.
[0165] The invention also relates to a light emitting device
comprising an electro-luminescent film comprising a substrate and
semiconductor nanoparticles on the substrate according to a
periodic pattern, wherein semiconductor nanoparticles have an
aspect ratio greater than 1.5; wherein the repetition unit of the
pattern has a smallest dimension of less than 500 micrometer and
comprises at least one pixel. All embodiments of the
electro-luminescent film of the invention may be implemented in
said light emitting device.
[0166] While various embodiments have been described and
illustrated, the detailed description is not to be construed as
being limited hereto. Various modifications can be made to the
embodiments by those skilled in the art without departing from the
true spirit and scope of the disclosure as defined by the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0167] FIG. 1 illustrates a schematic of an electro-luminescent
film (1) comprising a substrate (2). A periodic pattern (here a
rectangular lattice) is shown as a network of dotted lines. At each
node of the network, a repetition unit (3) of rectangular shape is
shown (delimited by a bold dotted line). Smallest size of
repetition unit is noted S. In repetition unit are shown three
pixels of square section (4a), (4b) and (4c). Semiconductor
nanoparticles (not shown) are on the substrate (2), in the volume
of each pixel.
[0168] FIG. 2 illustrates an anisotropic nanoparticle, here a
nanoplatelet, and defines aspect ratio.
[0169] FIG. 3 shows microscopy images of nanoplatelets used in
example 1. Scale bars are 10 nm (3a), 10 nm (3b) and 5 nm (3c).
[0170] FIG. 4 shows emission spectrum (arbitrary unit) of
nanoplatelets used in example 1 (emitting in red range: dashed
line, green range: dotted line and blue range: solid line) as a
function of light wavelength (.lamda. in nanometer).
EXAMPLES
[0171] The present invention is further illustrated by the
following examples.
Example 1
[0172] Preparation of a Stamp:
[0173] A photolithographic mask is fabricated on a UV-blue
transparent substrate to reproduce a pattern with squared pixels of
5 .mu.m size distributed on a square lattice of period 15 .mu.m. A
silicon carrier is covered by a uniform photolithography resin and
illuminated by an UV lamp producing a 350 nm light filtered by the
lithography mask in order to impress the pattern on the carrier. A
proper washing solution for the resin is utilized to develop the
polymer and create a tridimensional motif (pixelization).
[0174] A PDMS solution is casted on this tridimensional motif and
the silicon carrier, then heated at 150.degree. C. for 24 h to
assure the polymerization of the PDMS. The solidified PDMS is thus
separated from the silicon carrier. The so patterned PDMS is gold
covered by evaporation technique to ensure a conductive pixelated
surface. The patterned and conductive PDMS substrate is now called
the stamp. It consists of a planar conductive surface on which
square pixels of 5 .mu.m size and 20 .mu.m height are distributed
on a square lattice. The stamp is a square of size 5 cm.
[0175] Preparation of Substrate:
[0176] A p-doped silicon wafer substrate of 375 .mu.m thickness is
used to cast by spin coating a 200 nm thick PMMA solid film by
using a solution of 5% in weight of PMMA (Mw: 10.sup.6 gmol.sup.-1)
in toluene.
[0177] Preparation of Nanoparticles Colloidal Dispersions:
[0178] A solution A comprising 10.sup.-8 moleL.sup.-1
CdSe.sub.0.45S.sub.0.55/CdZnS/ZnS nanoplatelets in cyclohexane is
prepared. These nanoplatelets are 25 nm long, 20 nm wide and 9 nm
thick (core: 1.2 nm; first shell: 2 nm; second shell: 2 nm) and
emit at 630 nm with FWHM of 20 nm.
[0179] A solution B comprising 10.sup.-8 moleL.sup.-1
CdSe.sub.0.10S.sub.0.90/ZnS/Cd.sub.0.20Zn.sub.0.80S nanoplatelets
in cyclohexane is prepared. These nanoplatelets are 25 nm long, 20
nm wide and 8.5 nm thick (core: 1.5 nm; first shell: 1 nm; second
shell: 2.5 nm) and emit at 530 nm with FWHM of 30 nm.
[0180] A solution C comprising 10.sup.-8 moleL.sup.-1 CdS/ZnS
nanoplatelets in cyclohexane is prepared. These nanoplatelets are
25 nm long, 20 nm wide and 3 nm thick (core: 0.9 nm; first shell: 1
nm) and emit at 445 nm with FWHM of 20 nm.
[0181] Emission spectra of semiconductor nanoparticles from
solution A, B and C are shown in FIG. 4.
[0182] Preparation of Electro-Luminescent Film:
[0183] The substrate is put in contact with the stamp in order to
create a capacitive system with the PMMA in the middle (between
stamp and p-doped silicon) as dielectric medium. A voltage of 50 V
is applied for 1 minute in order to create permanent electrical
polarization in the PMMA layer (electret material) only in
correspondence with the pixels of the stamp.
[0184] To maintain stable the charges on the electret, humidity
level of the environment is kept below 50%.
[0185] Substrate with electrically polarized PMMA layer is dipped
in solution A for 10 seconds then rinsed by a clean solvent and
dried by a gentle flux of nitrogen.
[0186] Using a microscopic technique of alignment, the stamp is
then again placed on the already red pixelated substrate, with
pixels of the stamp defining a second pixel on the substrate
(different from the red pixel) according to the original periodic
patterning chosen. A voltage of 50 V is applied again for 1 minute
in order to create permanent electrical polarization in the PMMA
layer only in correspondence with the pixels of the stamp, i.e. in
correspondence with areas free of nanoparticles.
[0187] Substrate with electrically polarized PMMA layer is dipped
in solution B for 10 seconds then rinsed by a clean solvent and
dried by a gentle flux of nitrogen.
[0188] Using the same microscopic technique of alignment, the stamp
is then again placed on the already red/green pixelated substrate,
with pixels of the stamp defining a third pixel on the substrate
(different from the red and green pixels) according to the original
periodic patterning chosen. A voltage of 50 V is applied again for
1 minute in order to create permanent electrical polarization in
the PMMA layer only in correspondence with the pixels of the
stamp.
[0189] Substrate with electrically polarized PMMA layer is dipped
in solution C for 10 seconds then rinsed by a clean solvent and
dried by a gentle flux of nitrogen.
[0190] Electro-Luminescent Film and Device:
[0191] A 25 cm.sup.2 substrate of p-doped silicon coated with a 200
nm PMMA layer with square pixels of 5 .mu.m size and three
different types (red, green and blue emitting semiconductor
nanoparticles) distributed on a square lattice of period 15 .mu.m
is obtained, forming an electro-luminescent film.
[0192] Below the substrate, all necessary other layers and
electrical contacts needed for the injection of electric current in
each pixel are built by well know techniques in the microelectronic
industry of semiconductors, yielding an electro-luminescent
device.
Example 2
[0193] Example 1 is reproduced, except that periodic pattern is
changed.
[0194] In example 2a, pixels are square with 3 .mu.m size and
square lattice has a period of 12 .mu.m.
[0195] In example 2b, four squared pixels of size 5 .mu.m are
defined on a square lattice of period 15 .mu.m, with one red pixel,
two green pixels and one blue pixel.
Example 3
[0196] Example 1 is reproduced, except that substrate is
changed.
[0197] Example 3a: Silicon On Insulator (SOI) having the following
structure: Silicon (15 nm)-Insulator (200 nm)-Silicon (200 nm) is
used.
[0198] Example 3b: on a glass substrate with TFT matrix are
deposited successively the following layers: [0199] 1. a common
buried electrode for the periodic array of capacitance in step 3;
[0200] 2. a 300 nm silicon oxide insulator; [0201] 3. a periodic
array of separately isolated bottom electrode (each configured to
make a diode); and [0202] 4. optionally an electron transporting
layer for each pixel.
[0203] Example 3c: a LCD glass substrate with TFT matrix are
deposited successively the following layers: [0204] 1. a periodic
array of bottom electrode; [0205] 2. a ZnO electron transporting
layer for each pixel; and [0206] 3. a PMMA layer of 7 nm.
[0207] The same deposition method yields electro-luminescent films
which can be implemented as electro-luminescent devices using well
know techniques in the microelectronic industry of
semiconductors.
Example 4-1
[0208] Example 1 is reproduced, except that semiconductor
nanoparticles are changed.
[0209] A solution D comprising 10.sup.-8 moleL.sup.-1
CdSe.sub.0.45S.sub.0.55/Cd.sub.0.30Zn.sub.0.70S/ZnS nanoplatelets
in cyclohexane is prepared. These nanoplatelets are 35 nm long, 25
nm wide and 10.2 nm thick (core: 1.2 nm; first shell: 2.5 nm;
second shell: 2 nm) and emit at 630 nm with FWHM of 25 nm.
[0210] After dipping of substrate with electrically polarized PMMA
layer in solution D instead of solution A, nanoparticle deposition
is observed as for example 1. It is observed that deposition is
obtained in shorter exposure time, namely 4 seconds instead of 10
seconds.
Example 4-2
[0211] Example 1 is reproduced, except that semiconductor
nanoparticles are changed.
TABLE-US-00001 TABLE I Colloidal dispersions of semiconductor
nanoparticles used for deposition on substrate. (MLs refers to the
number of monolayers of inorganic material covering the core).
Dimensions L W T [NPs] Emission Nanoparticles (NPs) (nm) (nm) (nm)
(mol L.sup.-1) peak FWHM Deposition CORE/SHELL NANOPLATELETS
CdS/ZnS 5 MLs 17 17 3.2 5 .times. 10.sup.-6 465 nm 14 nm observed
CdS/ZnSe.sub.0.5S.sub.0.5 5 MLs 15 15 3.2 2 .times. 10.sup.-6 465
nm 15 nm observed CdS/ZnSe 5 MLs 17 17 3.5 1 .times. 10.sup.-6 460
nm 15 nm observed CdSe.sub.0.30S.sub.0.70/ZnS 5 MLs 25 20 3.1 0.2
.times. 10.sup.-6 535 nm 28 nm observed
CdSe.sub.0.25S.sub.0.75/Cd.sub.0.05Zn.sub.0.95S 27 22 3.4 2 .times.
10.sup.-6 550 nm 30 nm observed CdSe.sub.0.20S.sub.0.80/ZnSe 5 MLs
24 18 3.0 2 .times. 10.sup.-6 540 nm 29 nm observed
CdSe.sub.0.20S.sub.0.80/ZnSe.sub.0.50S.sub.0.50 26 20 3.3 0.5
.times. 10.sup.-6 530 nm 30 nm observed 5 MLs
CdSe.sub.0.83S.sub.0.17/Cd.sub.0.50Zn.sub.0.50S 28 18 5 1 .times.
10.sup.-6 621 nm 29 nm observed 4 MLs CdSe/Cd.sub.0.1Zn.sub.0.9S 4
MLs 16 17 4.9 2 .times. 10.sup.-6 625 nm 22 nm observed
CdSe.sub.0.75S.sub.0.25/Cd.sub.0.50Zn.sub.0.50S 30 20 4.8 4 .times.
10.sup.-6 645 nm 26 nm observed 4 MLs CdSe/ZnSe.sub.0.50S.sub.0.50
4 MLs 17 17 4 2 .times. 10.sup.-6 645 nm 28 nm observed CdSe/ZnS 4
MLs 17 17 4 3.5 .times. 10.sup.-6 617 nm 27 nm observed
CORE/SHELL/SHELL NANOPLATELETS ZnSe/ZnSe.sub.0.4S.sub.0.6/ZnS 50 20
3.2 20 .times. 10.sup.-6 445 nm 15 nm observed
CdSe.sub.0.90S.sub.0.10/ZnSe/ZnS 27 19 5 2 .times. 10.sup.-6 650 nm
28 nm observed 4 MLs CORE/CROWN NANOPLATELETS CdSe/CdS 3 MLs 20 12
0.9 3 .times. 10.sup.-6 465 nm 10 nm observed CdS/ZnSe 5 MLs 15 15
1.2 2 .times. 10.sup.-6 468 nm 15 nm observed CdSe/CdS 4 MLs 15 15
1.2 2 .times. 10.sup.-6 515 nm 10 nm observed
CdSe.sub.0.90S.sub.0.10/CdS 5 MLs 27 21 1.5 2.5 .times. 10.sup.-6
540 nm 14 nm observed CdSe/CdS 5 MLs 26 17 1.5 1 .times. 10.sup.-6
555 nm 12 nm observed DOT IN PLATE NANOPLATELETS (core: quantum
dot, final nanoparticle: nanoplatelet) CdSe/CdS 3 MLs 15 15 0.9 2.3
.times. 10.sup.-6 462 nm 10 nm observed
CdSe.sub.0.50S.sub.0.50/CdS/ZnS 25 25 3.2 2 .times. 10.sup.-6 540
nm 35 nm observed 4 MLs CORE/CROWN/SHELL NANOPLATELETS CdS/ZnSe/ZnS
5 MLs 17 17 3.5 2 .times. 10.sup.-6 550 nm 30 nm observed
CdSe.sub.0.30S.sub.0.70/CdS/ZnS 27 20 3.4 10 .times. 10.sup.-6 550
nm 30 nm observed 5 MLs
[0212] After dipping of substrate with electrically polarized PMMA
layer in a colloidal dispersion of semiconductor nanoparticles
listed in Table I instead of solution A, nanoparticle deposition is
observed as for example 1.
Example 5
[0213] Example 1 is reproduced, except that substrate and
preparation of electro-luminescent film are changed.
[0214] Substrate is a 50 .mu.m thick square glass slide of size 5
cm. Substrate is held horizontally.
[0215] The stamp is placed below the substrate and in contact with
the substrate. A voltage of 50 V is applied in order to induce
electrical polarization in the substrate only in correspondence
with the pixels of the stamp.
[0216] While voltage is applied, a layer of solution A is poured on
the top side of substrate and voltage is maintained for 10 seconds
then shut off. Stamp is removed from bottom side of substrate and
excess solution A is removed. Substrate is then rinsed by a clean
solvent and dried by a gentle flux of nitrogen.
[0217] Using a microscopic technique of alignment, the stamp is
then again placed below the already red pixelated substrate, with
pixels of the stamp defining a second pixel on the substrate
(different from the red pixel) according to the original periodic
patterning chosen. A voltage of 50 V is applied in order to induce
electrical polarization in correspondence with the pixels of the
stamp.
[0218] While voltage is applied, a layer of solution B is poured on
the top side of substrate and voltage is maintained for 10 seconds
then shut off. Stamp is removed from bottom side of substrate and
excess solution B is removed. Substrate is then rinsed by a clean
solvent and dried by a gentle flux of nitrogen.
[0219] Using the same microscopic technique of alignment, the stamp
is then again placed below the already red/green pixelated
substrate, with pixels of the stamp defining a third pixel on the
substrate (different from the red and green pixels) according to
the original periodic patterning chosen. A voltage of 50 V is
applied in order to induce electrical polarization in
correspondence with the pixels of the stamp.
[0220] While voltage is applied, a layer of solution C is poured on
the top side of substrate and voltage is maintained for 10 seconds
then shut off. Stamp is removed from bottom side of substrate and
excess solution C is removed. Substrate is then rinsed by a clean
solvent and dried by a gentle flux of nitrogen.
Comparative Example C1
[0221] Example 1 is reproduced, except that semiconductor
nanoparticles are changed.
[0222] A solution C-A comprising 10.sup.-8 moleL.sup.-1
CdSe/CdS/ZnS nanoparticles in cyclohexane is prepared. These
nanoparticles are spherical (aspect ratio of 1) with a diameter of
6 nm and emit at 620 nm with FWHM of 45 nm.
[0223] A solution C-B comprising 10.sup.-8 moleL.sup.-1
Cd.sub.0.10Zn.sub.0.90Se.sub.0.10S.sub.0.90/ZnS nanoparticles in
cyclohexane is prepared. These nanoparticles are spherical (aspect
ratio of 1) with a diameter of 6 nm and emit at 540 nm with FWHM of
37 nm.
[0224] After dipping of substrate with electrically polarized PMMA
layer in solution C-A instead of A, no significant nanoparticle
deposition is observed: isolated nanoparticles are found on the
substrate, but they do not form a layer of nanoparticles. No
selective deposition on the pattern occurs.
[0225] After dipping of substrate with electrically polarized PMMA
layer in solution C-B instead of B, no significant nanoparticle
deposition is observed: isolated nanoparticles are found on the
substrate, but they do not form a layer of nanoparticles. No
selective deposition on the pattern occurs.
[0226] Nanoparticles of solutions C-A and C-B are too small to form
significant deposits on substrate.
[0227] Thus, the deposit with spherical nanoparticles of this size
is not conclusive.
[0228] In addition, spherical nanoparticles emitting light in
shorter wavelength, typically in blue range, are even smaller in
diameter and it was not able to deposit these nanoparticles.
Comparative Example C2
[0229] Example 1 is reproduced, except that semiconductor
nanoparticles are changed.
[0230] A solution C-C comprising 10.sup.-8 moleL.sup.-1
CdSe/CdS/ZnS nanoparticles in cyclohexane is prepared. These
nanoparticles are spherical (aspect ratio of 1) with a diameter of
3 nm and emit at 620 nm with FWHM of 45 nm.
[0231] A solution C-D comprising 10.sup.-8 moleL.sup.-1
Cd.sub.0.10Zn.sub.0.90Se.sub.0.10S.sub.0.90/ZnS nanoparticles in
cyclohexane is prepared. These nanoparticles are spherical (aspect
ratio of 1) with a diameter of 4 nm and emit at 540 nm with FWHM of
37 nm.
[0232] After dipping of substrate with electrically polarized PMMA
layer in solution C-C instead of A, no significant nanoparticle
deposition is observed: isolated nanoparticles are found on the
substrate, but they do not form a layer of nanoparticles. No
selective deposition on the pattern occurs.
[0233] After dipping of substrate with electrically polarized PMMA
layer in solution C-D instead of B, no significant nanoparticle
deposition is observed: isolated nanoparticles are found on the
substrate, but they do not form a layer of nanoparticles. No
selective deposition on the pattern occurs.
[0234] Thus, nanoparticles of solutions C-C and C-D do not form
significant deposits on substrate because they are too small.
Comparative Example C3
[0235] Example 1 is reproduced, except that semiconductor
nanoparticles are changed.
[0236] A solution C-E comprising 10.sup.-8 moleL.sup.-1 of
composite particles comprising CdSe.sub.0.45S.sub.0.55/CdZnS/ZnS
nanoplatelets in SiO.sub.2 matrix, in cyclohexane is prepared
(nanoplatelets are 25 nm long, 20 nm wide and 9 nm thick). These
composite particles are spherical (aspect ratio of 1) with a
diameter of 100 nm and emit at 630 nm with FWHM of 20 nm.
[0237] A solution C-F comprising 10.sup.-8 moleL.sup.-1 of
composite particles comprising
CdSe.sub.0.10S.sub.0.90/ZnS/Cd.sub.0.20Zn.sub.0.80S nanoplatelets
in Al.sub.2O.sub.3 matrix, in cyclohexane is prepared. These
composite particles are spherical (aspect ratio of 1) with a
diameter of 120 nm and emit at 530 nm with FWHM of 30 nm.
[0238] After dipping of substrate with electrically polarized PMMA
layer in solution C-E instead of A, significant nanoparticle
deposition is observed.
[0239] After dipping of substrate with electrically polarized PMMA
layer in solution C-F instead of B, significant nanoparticle
deposition is observed.
[0240] However, the deposition of composite particles of solutions
C-E and C-F does not result in an electro-luminescent film because
SiO.sub.2 and Al.sub.2O.sub.3 encapsulating the semiconductor
nanoplatelets act as insulating, thus no electricity can be
transferred directly to the semiconductor nanoplatelets.
* * * * *